To my surprise (and delight) I actually got a reply from National Rail querying expiry dates on railcards; see my post #16. This is what they say verbatim:
Hello Peter,
Thanks for taking the time to email us. My sincere apologies for the delayed response. I understand that you are seeking clarification on the expiry of a Railcard.
As per our Terms and conditions, I would like to inform you that the start date and the end date on the Railcard are system generated; therefore, when the date changes at midnight, the system recognises the new date as its expiry date. Hence, your Railcard becomes inactive.
While I realise that this is not the answer you were hoping for, I trust I was able to clarify the situation.
If you have any other queries, please let me know if I can be of any further help.
Kind regards,
Santosh Khanvilkar
The Railcard Help Team
At least the reply is written in a more coherent way. Looks like it's all down to the "system" and that's that.